Abstract Detail

A New Genus of Holoparasitic Orobanchaceae Endemic to Guerrero, Mexico.

Recent field and herbarium studies have resulted in the discovery of a new, achlorophyllous, root-parasitic angiosperm. This perennial taxon apparently is endemic to a small area on the inland side of the Sierra Madre del Sur in Guerrero, Mexico. It parasitizes large lateral roots of mature trees of Hedyosmum mexicanum (Chloranthaceae) in steep-walled, headwater ravines dominated by montane evergreen tropical hardwoods. These drainages are isolated in a matrix of otherwise mainly pine-oak forest on adjacent slopes. Morphological features that ally the new taxon with the Orobanchaceae include: 1) the parasitic habit; 2) details of corolla shape and aestivation; 3) production of 4 stamens with loosely connivent anthers; 4) parietal placentation; 5) a hollow style terminating in a discoid-crateriform stigma with a central pore; 6) seeds with a prominent, loose, reticulate outer testa in which the enlarged cells rupture into concave, polygonal facets. However, the new taxon is amply distinct within the family and is discussed as a new genus and species. Autapomorphies that result in an expansion of the morphological circumscription of Orobanchaceae include: 1) the strongly 5-ribbed ovary and fruit; 2) production of 5 (vs. 2 or 4) parietal placentae; 3) unusual anthers in which the pollen sacs are more or less embedded in the expanded filament apex; 4) regularly pantohexaporate pollen grains.